‘bronze’ OA – free to read on the publisher’s webpage but without a license permitting free re-use of content

closed access – all other articles.

The most common form of OA was ‘bronze’. This may have implications for research; the lack of a license permitting the free re-use of an article’s contents can substantially restrict the impact of the data therein, for example by preventing other groups from conducting further analyses. In a recent Nature Index article, Piwowar notes that in the current age of machine learning and ‘big data’, it is especially important that data are freely available for computational analysis. Overall, the study found that 47% of articles were OA in 2015 (the most recent year of analysis), and the authors predict that all articles could be OA by 2040. Despite this encouraging forecast, the future of OA may be less bright if bronze OA continues to prevail.